1. Field of the Invention
This invention relates to a parking mechanism placed in a transmission.
2. Description of the Related Art
Generally, automatic transmissions are equipped with a parking mechanism inside thereof. The parking mechanism is formed of a parking gear, a parking sprocket plug, and a parking rod, etc. The parking gear is connected to an output shaft of the transmission. The parking sprocket plug has a pawl portion to be engaged with the parking gear.
When the transmission is set to a parking range by operation of a shift control lever, the parking rod oscillates the parking sprocket plug, and the pawl portion is engaged with the parking gear. Thereby, the output shaft of the transmission is fixed by the parking sprocket plug, and the axle shaft of the parking vehicle is fixed.
On the other hand, there are cases where the parking sprocket plug is provided with a return spring and/or a weight. These return spring and the weight urge the parking sprocket plug in a direction away from the parking gear. Jpn. Pat. Appln. KOKAI Pub. No. 200-178891discloses an example in which a weight is used for a parking sprocket plug.
However, when the urging force by the return spring and the weight is weak, the parking sprocket plug may be oscillated by vibration of the like, and may be accidentally engaged with the parking gear. On the other hand, if the spring force is increased, the power necessary for operating the parking sprocket plug is increased, and operation of the shift control lever requires much force.
Further, even when the parking sprocket plug is equipped with a weight, a return spring is also provided to suppress oscillation caused by vibration. Therefore, both weight of the weight and spring force of the return spring act on the parking sprocket plug, and there is the fear that operation of the shift control lever requires much force, and that a large force is applied on the parking mechanism.